Polysiloxane-containing rubber composition

ABSTRACT

A rubber composition having improved properties containing a starting rubber (e.g., diene rubber) and a polysiloxane having the following alkoxysilyl group (I) and/or acyloxysilyl group (II) and having an average degree of polymerization of 3 to 10,000: 
     
       
         ≡Si—OR 1   (I) 
       
     
     
       
         ≡Si—OCOR 2   (II) 
       
     
     wherein, R 1  is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 18 carbon atoms or an organic group containing an ether bond and R 2  is hydrogen or a hydrocarbon group having 1 to 21 carbon atoms.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polysiloxane-containing rubbercomposition having improved properties and a rubber compounding agenttherefor.

2. Description of the Related Art

Rubber compositions comprising various rubbers and a filler such assilica are known in the art and are used, for example, as rubbercompositions for tire treads having a low heat generation characteristicand superior in abrasion resistance etc. However, tire treads in whichsilica is formulated have a low rolling resistance and a good grip onwet roads, but there were the problems that the viscosity of theunvulcanized compound increases, the vulcanization is slowed, thekneading performance in the mixing falls, etc. and the productivitydeteriorates. Various proposals have been made in the past to solvethese problems, but unfortunately these are not practicallysatisfactory.

For example, it has been proposed to add diethylene glycol or a fattyacid (for example, see Gomu Kogyo Binran (or Rubber Industry Handbook),fourth version, pp. 517 to 518, published 1994), to add a metal salt ofa carboxylic acid (for example, see Tire Technology International 1995,pp. 107 to 108), and to treat the silica in advance with silicone oil(for example, see Japanese Unexamined Patent Publication (Kokai) No.6-248116). Further, the only way to deal with scorching during mixingand a fall in the kneading performance is to increase the number oftimes of mixture. Further, even when mixing carbon and silica, thepractice is to either mix them separately or to increase the mixing timeor frequency of mixture. None of these are unfortunately practicallyacceptable.

On the other hand, various metal oxides are used in many fields such asrubber, cosmetics, synthetic resins, coating compositions, adhesives,magnetic tapes. In most cases, since the metal oxides are added toorganic materials, problems arise how the metal oxides are dispersed inthe organic materials. For this purpose; various attempts have been madeto solve these problems. For example, the treatment of the metal oxideswith surface treatment agents has been proposed. JP-A-8-48910 disclosesa method for treating a metal oxide with methyl hydrogen polysiloxane,in which the metal oxides are necessary for treating at a hightemperature. JP-A-8-53630 discloses the treatment with an alkoxy silane,but this is not still sufficient.

On the other hand, rubber compositions comprising various rubbers andmetal oxides such as silica, clay, talc are known and are used as, forexample, rubber compositions for tire tread having excellent low heatbuild-up and abrasion resistance. However, when metal oxides arecompounded, there are disadvantages, when compared in the case of carbonblack, the modulus is decreased and the abrasion resistance is low. Tosolve these problems, the above-mentioned JP-A-6-248116 has beenproposed. (i.e., silica is surface-treated under heating with, forexample, a hydrophobic agent such as silicone oil comprising an organicsilicon compound at, for example, 250° C. for 1 hour. However, thismethod has a disadvantage of a short scorching due to heating at a hightemperature.

SUMMARY OF THE INVENTION

Accordingly, the objects of the present invention are to eliminate theabove-mentioned disadvantageous of the prior art and to provide afiller-containing vulcanizing rubber composition which improves theprocessability of the unvulcanized rubber composition, withoutsubstantially impairing the properties of the filler-containingvulcanized rubber composition such as the low heat generationcharacteristic and the abrasion resistance.

Another object of the present invention is to provide a rubbercompounding agent improving the vulcanized physical properties of asilica-containing vulcanizing rubber composition, in particular themodulus, abrasion resistance, and tanδ balance etc. and asilica-containing vulcanizing rubber composition using the same.

A further object of the present invention is to provide asurface-treated metal oxide capable of increasing the reinforceabilitywhen compounding into rubber and of improving the modulus and theabrasion resistance of the rubber composition and a rubber compositioncontaining the same.

A still further object of the present invention is to provide asilica-containing vulcanizing rubber composition for a tire tread whichimproves the processability of the unvulcanized rubber composition,without substantially impairing the properties of the silica-containingvulcanizing rubber composition, for example, the low heat generationcharacteristic and the abrasion resistance.

Other objects and advantages of the present invention will be apparentfrom the following description.

In accordance with the present invention, there is provided a rubbercomposition comprising a filler, said rubber composition containing apolysiloxane having the following alkoxysilyl group (I) and/oracyloxysilyl group (II) and having at least six alkoxy groups or atleast two acyloxy groups directly bonded to the Si atom in the moleculethereof and having an average degree of polymerization of 3 to 10,000:

≡Si—OR¹  (I)

 ≡Si—OCOR²  (II)

wherein, R¹ is a substituted or unsubstituted monovalent hydrocarbongroup having 1 to 18 carbon atoms or an organic group containing anether bond and R² is hydrogen or a hydrocarbon group having 1 to 21carbon atoms.

In accordance with the present invention, there is provided a rubbercompounding agent comprising (A) a polysiloxane having the followingalkoxysilyl group (I) and/or acyloxysilyl group (II) and having anaverage degree of polymerization of 3 to 10,000 and (B) a silanecoupling agent in a ratio of (A)/(B)=95/5 to 5/95:

≡Si—OR¹  (I)

≡Si—OCOR²  (II)

wherein, R¹ is a substituted or unsubstituted monovalent hydrocarbongroup having 1 to 18 carbon atoms or an organic group containing anether bond and R² is hydrogen or a hydrocarbon group having 1 to 21carbon atoms.

In accordance with the present invention, there is further provided arubber composition comprising 100 parts by weight of a starting rubber,5 to 100 parts by weight of silica, and an amount of the above-mentionedrubber compounding agent to give a content of the polysiloxane containedtherein of 0.2 to 30% by weight in the total composition.

In accordance with the present invention, there is further provided apolysiloxane surface-treated metal oxide comprising 100 parts by weightof a metal oxide surface treated with 0.1-50 parts by weight of apolysiloxane having the following alkoxysilyl group (I) and/oracyloxysilyl group (II) and having an average degree of polymerizationof 3 to 10,000:

≡Si—OR¹  (I)

≡Si—OCOR²  (II)

wherein, R¹ is a substituted or unsubstituted monovalent hydrocarbongroup having 1 to 18 carbon atoms or an organic group containing anether bond and R² is hydrogen or a hydrocarbon group having 1 to 21carbon atoms.

In accordance with the present invention, there is further provided arubber composition comprising 100 parts by weight of a starting rubberand 5 to 100 parts by weight of the above-mentioned polysiloxanesurface-treated metal oxide.

In accordance with the present invention, there is provided a rubbercomposition for a pneumatic tire tread comprising 100 parts by weight ofa diene rubber, 2 to 80 parts by weight of carbon black, 5 to 80 partsby weight of silica, a silane coupling agent, and a polysiloxane havingthe following alkoxysilyl group (I) and/or acyloxysilyl group (II) andhaving an average degree of polymerization of 3 to 10,000:

≡Si—OR¹  (I)

≡Si—OCOR²  (II)

wherein R¹ and R² are the same as defined above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term “filler” used herein means any conventional inorganic fillers(e.g., calcium carbonate, clay, talc, diatomaceous silica, mica,alumina, aluminum sulfate, barium sulfate, calcium sulfate, etc.) andso-called reinforcing agents, (e.g., carbon black, silica, etc.). Theterm “silica” used herein means wet silica and dry silica and silicahaving a nitrogen specific surface area of 50 to 400 m²/g. The use ofthe wet silica is preferable. Further, the term “vulcanization” usedherein includes cross-linking by sulfur, peroxide, etc. in addition tothe usual vulcanization by sulfur.

The first aspect of the present invention provides a rubber compositioncomprising a filler, said rubber composition containing a polysiloxanehaving the following alkoxysilyl group (I) and/or acyloxysilyl group(II) and having an average degree of polymerization of 3 to 10,000,preferably 10 to 1,000:

≡Si—OR¹  (I)

 ≡Si—OCOR²  (II)

wherein, R¹ is a substituted or unsubstituted monovalent hydrocarbongroup having 1 to 18 carbon atoms, preferably an alkyl group having 1 to6 carbon atoms and an aryl group having 6 to 12 carbon atoms, or anorganic group containing an ether bond, preferably R⁶(OR⁷)_(n) (whereinR⁶ is C₁-C₆ alkyl, R⁷ is C₂-C₄ alkylene, n is 1 to 3, R² is hydrogen ora hydrocarbon group having 1 to 21 carbon atoms, preferably C₁-C₂₁,alkyl or C₆-C₁₂ aryl which may be substituted with C₁-C₆ alkyl. Morepreferably, the polysiloxane has at least six alkoxy groups and/or atleast two acyloxy groups directly bonded to the Si atom in the moleculethereof.

According to a preferable embodiment of the present invention, there isprovided a rubber composition further containing in the rubbercomposition a silane coupling agent in an amount of 40% by weight orless of the silica content.

As explained above, there was the problem that the vulcanized propertiesof the tire tread containing silica were excellent, but theprocessability at the time when unvulcanized was poor. We have foundthat, this is due to the silanol groups (Si—OH) present on the surfaceof the silica. The cohesiveness of the silanol groups causes theproduction of structures in the rubber composition and the increase inthe viscosity, the polarity of the silanol groups causes thevulcanization accelerator etc. to be adsorbed and vulcanization to bedelayed, and the compatibility with the nonpolarized rubber isinsufficient, and therefore, the kneading performance in the mixing isdecreased. Due to these phenomena, the processability of theunvulcanized composition falls. Further, in many cases silane couplingagents can be jointly used in a silica-containing rubber composition toreinforce the rubber, but silanol groups are also present inside thesilica particles and there was the problem that these would react withthe silane coupling agent to cause a loss of the silane coupling agentand reduce the reinforcing effect, making inclusion of a large amount ofa silane coupling agent necessary. When diethylene glycol or otherpolarized substance is added to this, it is possible to prevent to acertain extent the phenomenon of adsorption of the vulcanizationaccelerator or other polarized compounding agents, but completeprevention is not possible and it was not possible to prevent thesubstances chemically bonding with a silane coupling agent or othersilica particles from bonding inside.

According to the present invention, since a polysiloxane having thealkoxysilyl groups and/or acyloxysilyl groups of the above formulae (I)and/or (II), respectively, is blended into the rubber composition, thealkoxysilyl groups (I) and/or acyloxysilyl groups (II) react with thesilanol groups and covers the surface of the silica particles, andtherefore, the problems in the prior art are solved and it is possibleto effectively suppress the rise in viscosity caused by the cohesivenessand polarity of the silanol groups and the wasted consumption of thevulcanization accelerator or other polarized additives or silanecoupling agent etc.

The polysiloxane containing the alkoxysilyl groups (I) and/oracyloxysilyl groups (II) blended in the rubber composition according tothe present invention, as mentioned above, must have an alkoxysilylgroup (I) and/or acyloxysilyl group (II) reacting with a silanol groupand be a polymer (or oligomer) of a size covering the surface of thesilica particles and exhibit a lubricating effect, for example, anaverage degree of polymerization of 3 to 10,000, preferably 10 to 1,000(or a number average molecular weight of 200 to 300,000, preferably 500to 50,000). Accordingly, in the polysiloxane of the present invention,it is essential that a ≡Si—O—R³ group and/or ≡Si—OCOR² group be present.These groups may be at the main chain, side chains, or ends. Inaddition, the presence of at least six alkoxy groups and/or at least twoacyloxy groups preferably directly bonded to the Si atom in one moleculethereof provides the strong bonding with the filler. Further, a hydrogengroup or other organic groups are also possible. The polysiloxane usablein the first aspect of the present invention preferably has at least onehydrocarbon group such as alkyl group directly bonded to the Si atom inthe molecule thereof in view of the affinity thereof with the rubbercomponent.

The polysiloxane is a known substance. For example, it may bemanufactured as follows:

The polysiloxane containing an alkoxysilyl or acyloxysilyl group issynthesized by causing a reaction between an Si—H group containingpolysiloxane and alcohol or carboxylic acid in the presence of acatalyst.

As the ≡Si—H group containing polysiloxane, the ones illustrated belowmay be mentioned:

As the alcohol usable in the present invention, methanol, ethanol,propanol, butanol, pentanol, heptanol, octanol, octadecanol, phenol,benzyl alcohol, and also ethylene glycol monomethyl ether, diethyleneglycol monomethyl ether, and other alcohols having oxygen atoms may beillustrated.

As the carboxylic acid, acetic acid, propionic acid, palmitic acid,stearic acid, myristic acid, etc. may be mentioned.

As the catalyst, chloroplatinic acid, platinum-ether complexes,platinum-olefin complexes, PdCl₂ (PPh₃)₂, RhCl₂ (PPh₃)₂, or basiccatalysts may be used. The corresponding ≡Si—H group containingpolysiloxane and alcohol or carboxylic acid are reacted in the presenceof the catalyst for synthesis.

As the method for introducing the organic group, introduction is easy bycausing a reaction of ≡Si—H and an organic compound having a doublebond. As a compound having a double bond, there are styrene,α-methylstyrene, α-methylstyrene dimer, limonene, vinylcyclohexene, etc.

As another method, synthesis is possible by causing a reaction between acorresponding ≡Si—H group containing polysiloxane and a double bondcontaining alkoxysilane as shown below in the presence of the abovecatalyst:

As still another method, the polysiloxane used in the present inventionmay be synthesized by causing a reaction between a silanol terminalpolysiloxane and an alkoxysilane in the presence of a bivalent tincompound or other catalyst. Examples of such a silanol terminalpolysiloxane are:

wherein n is 1 to 2000

Examples of the alkoxysilane, are the following alkoxysilanes. Further,the silane coupling agents shown in Table I are exemplified.

TABLE I Chemical name Structural formula VinyltrimethoxysilaneCH₂═CHSi(OCH₃)₃ Vinyltriethoxysilane CH₂═CHSi(OCH₂CH₃)₃ Vinyltris(2-CH₂═CHSi(OCH₂CH₂OCH₃)₃ methoxyethoxy)silane N-(2-aminoethyl)3-aminopropylmethyl- dimethoxysilane

N-(2-aminoethyl)3- H₂NCH₂CH₂NH(CH₂)₃Si(OCH₃)₃ aminopropyltrimethoxy-silane 3-aminopropyltrimethoxy- H₂N(CH₂)₃Si(OCH₃)₃ silane3-glycidoxypropyltri- methoxysilane

3-glycidoxypropylmethyl- dimethoxysilane

2-(3,4- epoxycyclohexyl)ethyl- trimethoxysilane

3-methacryloxypropyl- trimethoxysilane

3-mercaptopropyl- HS(CH₂)₃Si(OCH₃)₃ trimethoxylsilane 3-aminopropyl-H₂N(CH₂)₃Si(OCH₂CH₃)₃ triethoxysilane bis-[3-(triethoxysilyl)-propyl]tetrasulfide

The polysiloxane usable in the present invention may further besynthesized by a reaction between polysiloxane having a reactivefunctional group at its side chain or terminal and a silane couplingagent of Table I. Examples of the polysiloxane having a reactivefunctional group, are an epoxy group, amine group, mercapto group,carboxyl group, etc.

Note that the polysiloxane used in the present invention, as explainedabove, is not particularly limited in its terminal groups and sidechains and is determined by the type of the starting material usedduring manufacture.

The amount of the polysiloxane used in the first aspect of the presentinvention is preferably 100% by weight or less, preferably 1 to 100% byweight, particularly preferably 2 to 40% by weight, of the weight of thefiller in the rubber composition. When the content of the polysiloxaneis too small, the desired effect cannot be obtained, while conversely iftoo great, substances not bonding with the filler (e.g., silica) willleak out from the vulcanized product in some cases, which is notdesired.

Although there are no specific limitations to the amount of the fillerto be kneaded, preferably 5 to 150 parts by weight, more preferably 20to 120 parts by weight, particularly preferably 50 to 90 parts by weightof the filler based upon 100 parts by weight of the rubber component canbe used.

The rubber contained as the main ingredient in the vulcanizable rubbercomposition according to the present invention may be any rubbergenerally contained in various rubber compositions in the past, forexample, natural rubber (NR), polyisoprene rubber (IR), variousstyrene-butadiene copolymer rubbers (SBR), various polybutadiene rubbers(BR), acrylonitrile-butadiene copolymer rubbers (NBR), butyl rubber(IIR), and other diene rubbers or ethylene-propylene copolymer rubbers(EPR, EPDM) etc. alone or as any blends.

The vulcanizable rubber composition according to a preferred mode of thesecond aspect of the present invention further contains a silanecoupling agent. The silane coupling agent used in the present inventionmay be made any silane coupling agent used together with silica fillersin the past. The typical examples are shown in Table I. Of these,bis-[3-(triethoxysilyl)-propyl]tetrasulfide and the silane couplingagents shown in Table I′ below is most preferred from the viewpoint ofthe processability.

When a silane coupling agent is mixed into the vulcanizing rubbercomposition according to the present invention, it is possible to reducethe amount of the silane coupling agent used compared with the past andit is possible to further improve the abrasion resistance. Thepreferable amount of the silane coupling agent used in the presentinvention is 40% by weight or less, preferably 0.5 to 40% by weight,particularly preferably 1 to 20% by weight, based upon the amount of thesilica in the composition. When the amount of the silane coupling agentis too small, the desired effects cannot be obtained, while converselywhen too great, scorching will easily occur in the mixing or extrusionstep, which is not desirable.

According to the second aspect of the present invention, there isprovided a rubber compounding agent including (A) a polysiloxanecontaining the following alkoxysilyl group (I) and/or acyloxysilyl group(II) and having an average degree of polymerization of 3 to 10,000 and(B) a silane coupling agent in a ratio of (A)/(B)=95/5 to 5/95:

≡Si—OR¹  (I)

≡Si—OCOR²  (II)

wherein R¹ and R² are the same as explained above.

According to the second aspect of the present invention, there isprovided a rubber compounding agent wherein the polysiloxane (A) isimpregnated in (C) at least one powder in a ratio of (A)/(C)=70/30 to5/95.

According to the second aspect of the present invention, there isprovided a rubber composition comprising 100 parts by weight of thestarting rubber, 5 to 100 parts by weight of silica, and an amount ofthe rubber compounding agent composed of (A) and (B) or (A) and (C) togive a content of the polysiloxane contained therein of 0.2 to 30% byweight in the total composition.

As mentioned above, if a polysiloxane (A) having an alkoxysilyl group oracyloxysilyl group of the formula (I) or (II) is blended in a rubbercomposition, the alkoxysilyl groups (I) or the acyloxysilyl groups (II)react with the silanol groups and cover the surface of the silicaparticles, and therefore, the problems in the prior art are solved andit is possible to effectively suppress the rise in viscosity caused bythe cohesiveness and polarity of the silanol groups and the wastedconsumption of the vulcanization accelerator or other polarizedadditives or silane coupling agent etc. However, the silane couplingagent for increasing the reinforcing nature of the silica and thepolysiloxane for improving the processability of the silica both reactwith the silanol groups on the surface of the silica in competitivereactions. Thus, we found that the physical properties of the rubberdiffered depending on the method of mixture (or order). That is, if thesilica and polysiloxane react first, the reinforcing nature falls, whichis not desirable. Therefore, in the present invention, the couplingagent and polysiloxane are mixed in advance into the rubber, so reactionof just the polysiloxane first is prevented or the polysiloxane ispre-impregnated into carbon black or another nonreactive filler (i.e.,inert powder) or silica or another powder so as to delay the reactionwith the silica and thereby prevent a decline in the vulcanized physicalproperties of the rubber.

The polysiloxane (A) containing the alkoxysilyl groups (I) oracyloxysilyl groups (II) blended in the rubber composition according tothe present invention, as mentioned above, must have an alkoxysilylgroup (I) and/or acyloxysilyl group (II) reacting with a silanol groupand be a polymer (or oligomer) of a size covering the surface of thesilica particles and exhibit a lubricating effect, for example, anaverage degree of polymerization of 3 to 10,000, preferably 10 to 1,000.Accordingly, in the polysiloxane (A) used in the present invention, itis essential that a ≡Si—O—R¹ group or ≡Si—OCOR² group be present. Thesegroups may be at the main chain, side chains, or ends. Further, ahydrogen group or other organic group is also possible. The polysiloxaneis a known substance, as mentioned above.

The polysiloxane (A) used in the present invention may further besynthesized by a reaction between polysiloxane having a reactivefunctional group at its side chain or terminal and a silane couplingagent of Table I. As the polysiloxane having a reactive functionalgroup, mention may be made of an epoxy group, amine group, mercaptogroup, carboxyl group, etc., also as mentioned above.

Note that the polysiloxane (A) used in the present invention, asexplained above, is not particularly limited in its terminal groups andside chains and is determined by the type of the feedstock used duringmanufacture.

The polysiloxane (A) used in the present invention is mixed in to give0.2 to 30% by weight, preferably 1.0 to 10% by weight, based upon therubber composition. If the content of the polysiloxane (A) is too small,the desired effect cannot be obtained, while conversely if too great,substances not bonding with the silica will leak out from the vulcanizedproduct in some cases, which is not desired.

The rubber contained as the main ingredient in the vulcanizing rubbercomposition according to the present invention may be any rubbergenerally contained in various rubber compositions in the past, asmentioned above.

The silane coupling agent (B) used in the vulcanizing rubber compositionof the present invention may be made any silane coupling agent usedtogether with silica fillers in the past. As typical examples, any agentshown in Table I may be mentioned. Of these,bis-[3-(triethoxysilica)-propyl]tetrasulfide and the silane couplingagents shown in Table I′ below is most preferred from the viewpoint ofthe processability.

If a silane coupling agent (B) is mixed into the vulcanizing rubbercomposition according to the present invention, it is possible to reducethe amount of the silane coupling agent (B) used compared with the pastand it is possible to further improve the abrasion resistance. Thepreferable amount of the silane coupling agent (B) used in the presentinvention is, in terms of a ratio (ratio by weight) of the polysiloxane(A) in the composition and the silane coupling agent (B) of 95/5 to5/95, particularly preferably 60/40 to 80/20. If the amount of thesilane coupling agent (B) is too small, the desired effects cannot beobtained, while conversely if too great, scorching will easily occur inthe mixing or extrusion step, which is not desirable.

The rubber composition of the second embodiment according to the secondaspect of the present invention is composed of at least one powder (C)generally mixed with rubber compositions in the past mixed with thepolysiloxane (A). Examples of the powder (C) are carbon black, calciumcarbonate, stearic acid, and other inert powders, silica, etc. Here,“inert powder” means a powder with a small reactivity with thepolysiloxane (A) of the present invention. The amount of this inertpowder (C) is, in terms of the ratio of weight of (A)/(C), 70/30 to5/95, more preferably 60/40 to 30/70. If the amount of the inert powderis too small, the silica and polysiloxane will react overly fast,whereby the reinforcing property will fall, which is not desirable,while conversely when too great, the effect of surface treatment of thepolysiloxane on the silica will become smaller, which is also notdesirable. The method of impregnation of the polysiloxane (A) to thepowder (C) is not particularly limited, but use may be made of a mixer,kneader, mill, etc. usually used according to need.

The silica-containing rubber composition according to the presentinvention is composed of 5 to 100 parts by weight, preferably 5 to 80parts by weight, of rubber use silica based upon 100 parts by weight ofthe starting rubber and an amount of the rubber compounding agent (thatis, the premix of the polysiloxane (A) and the silane coupling agent (B)or powder (C)) so as to give 0.2 to 30% by weight, preferably 1 to 10%by weight, of polysiloxane (A) in the total composition.

The third aspect of the present invention provides a polysiloxanesurface-treated metal oxide comprising 100 parts by weight of a metaloxide surface treated with 0.1-50 parts by weight of a polysiloxanehaving the following alkoxysilyl group (I) or acyloxysilyl group (II)and having an average degree of polymerization of 3 to 10,000:

≡Si—OR¹  (I)

≡Si—OCOR²  (II)

wherein R¹ and R² are the same as explained above.

According to preferable embodiments of the third aspect, there isprovided a polysiloxane surface-treated metal oxide, wherein the metaloxide is SiO₂ or SiO₂-containing metal oxide or wherein 0.05 to 50% byweight of a titanium catalyst, based upon the amount of the polysiloxaneused, is further used during the surface treatment.

According to the third aspect, there is also provided a rubbercomposition comprising 100 parts by weight of a starting rubber and 5 to100 parts by weight of the above-mentioned polysiloxane surface-treatedmetal oxide, preferably silica and optionally a silane coupling agent inan amount of 0.5-40% by weight of the amount of the silica is furthercontained in the composition.

As mentioned above, the polysiloxane containing the alkoxysilyl groups(I) or acyloxysilyl groups (II) according to the present invention, asmentioned above, must have an alkoxysilyl group (I) or acyloxysilylgroup (II) reacting with a silanol group and be a polymer (or oligomer)of a size covering the surface of the silica particles and exhibit alubricating effect, for example, an average degree of polymerization of3 to 10,000, preferably 10 to 1,000. Accordingly, in the polysiloxane ofthe present invention, it is essential that a ≡Si—O—R¹ group or≡Si—OCOR² group be present. These groups may be at the main chain, sidechains, or ends. Further, a hydrogen group or other organic group isalso possible. The polysiloxane is a known substance and can besynthesized by the reaction between an Si—H group containingpolysiloxane and alcohol or carboxylic acid in the presence of acatalyst, as mentioned above.

The polysiloxane usable in the present invention may further besynthesized by a reaction between polysiloxane having a reactivefunctional group at its side chain or terminal and a silane couplingagent of Table I shown above. Examples of the polysiloxane having areactive functional group, are an epoxy group, amine group, mercaptogroup, carboxyl group, etc.

Note that the polysiloxane used in the present invention, as explainedabove, is not particularly limited in its terminal groups and sidechains and is determined by the type of the starting material usedduring manufacture. According to the present invention, the surface ofthe metal oxide is surface treated with the polysiloxane. The surfacetreating method is not specifically limited. Generally speaking, themetal oxide can be impregnated or coated with the polysiloxane at roomtemperature in an appropriate solvent (e.g., acetone, methanol,ethanol), followed by heat drying at room temperature to 120° C.

The amount of the polysiloxane to be used for the surface treatmentaccording to the present invention is generally 0.1 to 50 parts byweight, preferably 1 to 20 parts by weight. If the amount of thepolysiloxane is too small, the desired results cannot be obtained, whileconversely it too large, the polysiloxane which does not react with themetal oxide is unpreferably exdudated from the vulcanized product.

When the surface-treated metal oxide is added in an amount of 5-100parts by weight, preferably 10-80 parts by weight, to 100 parts byweight of the starting rubber, the desired reinforcing effects can beobtained. When the amount is less than 5 parts by weight, the desiredeffects of the present invention are not sufficient, while more than 100parts by weight, the processability unpreferably becomes poor.

Examples of the metal oxides according to the present invention aremetal oxides comprising a single metal such as silicon oxide, titaniumoxide, aluminum oxide, iron oxide, zirconium oxide, cerium oxide andcomplex or composite oxides such as calcium silicate, aluminum silicate,magnesium silicate, zeolite, feldspar, kaolinite, clay, talc. Here, asthe metal oxides conventionally used for rubber compounding, silicatefillers such as silicic anhydride, silicic hydrate, calcium silicate,aluminum silicate, kaolin, talc are preferable.

The titanium catalysts usable in the preferable embodiment of thepresent invention are titanium compounds such as alkoxy titanium,titanium chelate, titanium acylate, complex or composite titanate. Astypical examples, the titanium compounds TA-10 and TC-100 (availablefrom Matsumoto Koushou K.K. Japan) having the following structure can beeffectively used.

In the preferable embodiment of the third aspect of the presentinvention, the above titanium catalyst is used in an amount of 0.05 to50% by weight, more preferably 0.1 to 10% by weight, of the amount ofthe polysiloxane. If the amount is too small, the desired effect of thesurface treatment cannot be efficiently obtained, while conversely toolarge, the processability tends to be decreased when the rubbercomposition is prepared.

The rubber contained as the main ingredient in the vulcanizable rubbercomposition according to the present invention may be any conventionalrubber as mentioned previously.

The vulcanizable rubber composition according to a preferred mode of thethird aspect of the present invention may further contains a silanecoupling agent. The silane coupling agent usable in the presentinvention may be any silane coupling agent used together with silicafillers in the past. The typical examples, are shown in Table I.Further, the following special sulfur-containing silane coupling agentsshown in Table I′ below can also be used. Of these,bis-[3-(triethoxysilica)-propyl]tetrasulfide is most preferred from theviewpoint of the processability.

TABLE I′ Chemical name Structural formula 3-Trimethoxysilylpropyl-N,N-dimethyl thiocarbamoyl tetrasulfide

Trimethoxysilylpropyl- mercaptobenz-thiazole tetrasulfide

Thiethoxysilylpropyl- methacrylate monosulfide

Dimethoxymethylsilylpropyl- N,N-dimethylthiocarbamoyl tetrasulfide

When a silane coupling agent is mixed into the vulcanizing rubbercomposition according to the third aspect of the present invention, itis possible to improve the abrasion resistance. The preferable amount ofthe silane coupling agent usable in the present invention is 1 to 20% byweight, preferably 2 to 10% by weight, based upon the amount of thesilica in the composition. When the amount of the silane coupling agentis too small, the desired effects cannot be obtained, while converselywhen too large, scorching will easily occur in the mixing or extrusionstep, which is not desirable.

According to the fourth aspect of the present invention, there isprovided a rubber composition for a tire tread including 100 parts byweight of a diene rubber, 2 to 80 parts by weight, preferably 5 to 60parts by weight, of carbon black, 5 to 80 parts by weight, preferably 10to 50 parts by weight, of silica, a silane coupling agent, and thepolysiloxane mentioned below. Examples of such a polysiloxane hasrepeating units of the formula (III):

wherein, R³ represents independently a methyl group, ethyl group, orphenyl group, R⁴ indicates independently hydrogen or an organic group(e.g., methyl, phenylethyl, 2-(4-methyl-3-cyclohexenyl)-propyl,2,4-diphenyl-4-methylpentyl, R⁵ indicates independently an alkyl groupor acyl group, m is 0 or an integer of 1 or more, and n is an integer of1 or more.

In accordance with a preferred embodiment the fourth of the presentinvention, there is provided a rubber composition for a tire tread asmentioned above, wherein the amounts of the polysiloxane and silanecoupling agent are:

0.5≦(W_(PS)/W_(SC))≦7

Content of silica×1 wt %≦W_(PS)+W_(SC)≦

Content of silica×40 wt %

wherein, W_(PS): content of polysiloxane (parts by weight), and W_(SC):content of silane coupling agent (parts by weight).

According to a preferred embodiment of the fourth aspect of the presentinvention, there is provided a rubber composition for a tire tread asmentioned above, wherein the compound except for the vulcanizationsystem is obtained by mixing at a temperature of at least 120° C. in asimultaneous step.

As explained above, there was the problem that the vulcanized propertiesof the tire tread containing silica were excellent, but theprocessability at the time when unvulcanized was poor.

However, according to the present invention, since a polysiloxane havingthe repeating structural units of the above formula (III) is blendedinto the rubber composition, the alkoxysiloxane reacts with the silanolgroups and covers the surface of the silica particles, and therefore,the problems in the prior art are solved and it is possible toeffectively suppress the rise in viscosity caused by the cohesivenessand polarity of the silanol groups and the wasted consumption of thevulcanization accelerator or other polarized additives or silanecoupling agent etc.

The polysiloxane of the above formula (III) contained in the rubbercomposition according to the present invention, as mentioned above, musthave an alkoxysilyl group or acyloxysilyl group reacting with a silanolgroup and be a polymer (or oligomer) of a size covering the surface ofthe silica particles and exhibit a lubricating effect, for example, anaverage degree of polymerization of 3 to 10,000, preferably 10 to 1,000.Accordingly, in the repeating unit of the above formula (III), it isessential that a ≡Si—O—R³ group be present. Accordingly, n should be atleast 1, preferably 5 to 1000 and m may be zero, but a hydrogen group orother organic group is also possible. The polysiloxane is a knownsubstance. For example, it may be manufactured as follows:

The compound having the siloxane structure of formula (III) issynthesized by causing a reaction between the correspondingpolyalkylhydrogensiloxane and alcohol or carboxylic acid in the presenceof a catalyst. Examples of the polyalkylhydrogensiloxane are thosementioned above.

The polysiloxane used in the present invention, as explained above, isnot particularly limited in its terminal groups and is determined by thetype of the feedstock used during manufacture. For example, it may havea trimethylsilyl group, methyldiphenylsilyl group, triphenylsilyl group,and also organic groups.

In formula (III), as mentioned above, R¹ represents a methyl group,ethyl group, or phenyl group, and R² represents hydrogen or an organicgroup, for example, CH₃, C₂H₅, styrene residue, divinylbenzene residue,limonene residue, butadiene residue, isoprene residue, etc.

The diene rubber contained as the main ingredient in the vulcanizingrubber composition according to the present invention may be any dienerubber generally contained in various rubber compositions as mentionedabove.

The silane coupling agent used in the present invention may be made anysilane coupling agent used together with silica fillers in the past.Typical examples are shown in Table I above. Of these,bis-[3-(triethoxysilica)-propyl]tetrasulfide is most preferred from theviewpoint of the processability.

The amounts of the polysiloxane and silane coupling agent used in thepresent invention are a total weight of the polysiloxane and silanecoupling agent of 0.5 to 40% by weight, preferably 1 to 20% by weightbased upon the amount of the silica, and a weight ratio (ofpolysiloxane/silane coupling agent) of 0.5 to 7, preferably a range of 1to 4. If the amount of the polysiloxane is too small, the desiredeffects cannot be obtained, while conversely if too great, thesubstances not bonding with the silica will leak out from the vulcanizedproduct in some cases, which is not desirable.

Further, if the amount of the silane coupling agent is too small, thedesired effects cannot be obtained, while conversely if too great,scorching will easily occur in the mixing or extrusion step, which isnot desirable.

Note that when the silica and carbon black are mixed in the same step inaccordance with the preferred embodiment of the present invention,sufficient contact and reaction occur between the diene rubber andcarbon black and the mixing is promoted, but sufficient contact andreaction are not obtained between the diene rubber and silica due to thepolarity of the silanol groups on the surface of the silica andtherefore knitting, scorching, etc. occur at the time of mixture and thedispersion also becomes poor.

Further, when separately mixing the silica and carbon black, forexample, when mixing the silica in the first step and adding the carbonblack and other compounding agents in the second step, there is notsufficient promotion of mixture of the diene rubber and carbon black inthe second step and it is difficult to obtain the inherent reinforcementof the carbon black in some cases. As mentioned above, therefore,according to the present invention, by adding a silane coupling agentand the polysiloxane shown in formula (I), the knitting and scorching atthe time of mixing in a simultaneous step are improved and thedispersion promoted and it is possible to obtain the same or betterperformance as the case of mixing the silica and carbon by separatesteps.

The rubber composition according to the first aspect of the presentinvention may contain, in addition to the above-mentioned essentialingredients, a vulcanization or cross-linking agent, a vulcanization orcross-linking accelerator, various types of oils, an antiaging agent,reinforcing agent, plasticizer, softening agent, or other variousadditives generally mixed into general rubbers. The compounds arekneaded and vulcanized by general methods to make the composition whichmay then be used for vulcanization or cross-linking. The amounts ofthese additives added may be made the amounts generally added in thepast so long as they do not run counter to the object of the presentinvention.

EXAMPLES

The present invention will now be further illustrated by, but is by nomeans limited to, the following Examples.

Example I

The various polysiloxanes shown by general formula were synthesized bythe following general methods:

Polysiloxane 1

100 g of polymethylhydrogensiloxane (KF99, made by Shinetsu ChemicalIndustry) and 42.5 g of methanol were mixed, 40 μl of 1% isopropylalcohol solution of chloroplatinic acid was added, and a reaction wascaused at 80° C. for 10 hours to synthesize the polysiloxane 2.

Polysiloxane 2

100 g of polymethylhydrogensiloxane (KF99, made by Shinetsu ChemicalIndustry) and 60 g of ethanol were mixed, 40 μl of 1% isopropyl alcoholsolution of chloroplatinic acid was added, and a reaction was caused at80° C. for 10 hours to synthesize the polysiloxane 2.

Polysiloxane 3

To a mixture of 180 g of ethanol and 200 μl of a 1% isopropyl alcoholsolution of chloroplatinic acid was dropped 200 g ofpolymethylhydrogensiloxane (KF99, made by Shinetsu Chemical Industry)over 3 hours. The mixture was then caused to react at 80° C. for 10hours to synthesize the polysiloxane. After this, the excessive ethanolwas distilled off under reduced pressure.

Polysiloxane 4

100 g of polymethylhydrogensiloxane (KF99, made by Shinetsu ChemicalIndustry) and 60 g of ethanol were mixed, 40 μl of 1% isopropyl alcoholsolution of chloroplatinic acid was added, a reaction was caused at 80°C. for 8 hours, 68 g of styrene and 40 μl of 1% isopropyl alcoholsolution of chloroplatinic acid were added, and a reaction was caused atthe same temperature for 3 hours to synthesize the polysiloxane.

Polysiloxane 5

100 g of polymethylhydrogensiloxane (KF99, made by Shinetsu ChemicalIndustry) and 78 g of ethanol were mixed, 40 μl of 1% isopropyl alcoholsolution of chloroplatinic acid was added, a reaction was caused at 80°C. for 8 hours, 70 g of divinyl benzene and 40 μl of 1% isopropylalcohol solution of chloroplatinic acid were added, and a reaction wascaused at the same temperature for 3 hours to synthesize thepolysiloxane.

Polysiloxane 6

100 g of polymethylhydrogensiloxane (KF99, made by Shinetsu ChemicalIndustry) and 60 g of ethanol were mixed, 40 μl of 1% isopropyl alcoholsolution of chloroplatinic acid was added, a reaction was caused at 80°C. for 8 hours, 88 g of limonene and 40 μl of 1% isopropyl alcoholsolution of chloroplatinic acid were added, and a reaction was caused atthe same temperature for 3 hours to synthesize the polysiloxane.

The polysiloxanes 1 to 6 obtained above are deduced to have thefollowing structures:

(IV) Polysiloxane no. R R′ p:q (p + q) Remarks 1 H CH₃ 21:79 40 p = 0 2H C₂H₅ 21:79 40 3 — C₂H₅ — 40 4 Styrene residue C₂H₅ 10:90 40 5 Divinylbenzene C₂H₅ 10:90 40 residue 6 Limonene residue C₂H₅ 10:90 40

Polysiloxane 7

200 g of polymethylhydrogensiloxane (KF99, made by Shinetsu ChemicalIndustry) and 49 g of vinyltrimethoxysilane (KBM1003, made by ShinetsuChemical Industry) were mixed, 100 μl of 1% isopropyl alcohol solutionof chloroplatinic acid was added, and a reaction was caused at 80° C.for 5 hours to synthesize the polysiloxane.

Polysiloxane 8

100 g of silanol terminated polymethylhydrogensiloxane (molecular weightof 35000) and 20 g of tetramethoxysilane were mixed. To these was added0.5 g of stannous dioctylate as a catalyst. The reaction was caused at90° C. for 4 hours, followed by distilling off the residualtetramethoxysilane at the same temperature under reduced pressure.

Polysiloxane 9

100 g of hydrogen terminated polymethylsiloxane (molecular weight of726, Toshiba Silicone) and 40.8 g of vinyltrimethoxysilane (KBM1003,made by Shinetsu Chemical Industry) were mixed. To these was added 100μl of 1% isopropyl alcohol solution of chloroplatinic acid was added,and a reaction was caused at 80° C. for 5 hours to synthesize thepolysiloxane.

Polysiloxane 10

100 g of epoxy-modified silicone (made by Shinetsu Chemical Industry,X22-163A) and 47 g of γ-aminopropyltriethoxysilane were made to react at60° C. for 4 hours, then the unreacted γ-aminopropyltriethoxysilane wasdistilled off at 90° C. under reduced pressure to obtain thepolysiloxane.

Polysiloxane 11

The MS56 of the following formula made by Mitsubishi Chemical was usedas it was:

Polysiloxane 12

The polysiloxane having the following structure was synthesized.

The other ingredients used in the formulations of the following StandardExamples, Examples of the invention, and Comparative Examples were thefollowing commercially available products:

Natural rubber: RSS#1

SBR: Nipol NS116 (Nihon Zeon)

Silica: Nipsil AQ (Nihon Silica)

Silane coupling agent: Si69 (Degussa) (chemical name:bis-[3-(triethoxylsilyl)-propyl]tetrasulfide)

Carbon black: Seast KH (Tokai Carbon)

Powdered sulfur: 5% oil treated powdered sulfur

Antioxidant 6C: N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine

Vulcanization accelerator CZ: N-cyclohexyl-2-benzothiazylsulfenamide

Vulcanization accelerator DPG: Diphenylguanidine

Zinc oxide: Zinc White no. 3

Stearic acid: Industrial use stearic acid

Preparation of Samples

The components other than the vulcanization accelerator and the sulfurwere mixed in a 1.8 liter internal mixer for 3 to 5 minutes. Thevulcanization accelerator and sulfur were kneaded by an 8-inch open rollto the master batch discharged when reaching 165±5° C. to obtain therubber composition. The unvulcanized physical properties of the obtainedrubber composition were measured.

The composition was then pressed and vulcanized in a 15×15×0.2 cm moldat 160° C. for 20 minutes to prepare the desired test piece and thevulcanized physical properties were evaluated.

The test methods for the unvulcanized physical properties and vulcanizedphysical properties of the compositions obtained in the examples were asfollows:

Unvulcanized Physical Properties

1) Kneading performance at mixer: Evaluated by kneading performance ofmaster batch at time of discharge from mixer.

⊚ . . . Well kneaded mass with almost no powder not attached to rubber.

∘ . . . Well kneaded mass, but powder not attached to rubber seen atscattered locations.

X . . . Small pieces of free rubber with powder attached observed.

2) Mooney viscosity: Measured at 100° C. based on JIS K 6300.

3) Vulcanization rate: Time to reach 95% vulcanization at 160° C.measured based on JIS K 6300.

4) Scorching time: Time for viscosity to rise 5 points at 125° C.measured based on JIS K 6300.

Vulcanized Physical Properties

1) Sheet skin: The vulcanized sheet was observed visually and ones witha smooth surface and gloss were judged as good.

2) 300% modules, tensile strength at break, and elongation at break:Measured in accordance with JIS K 6251 (dumbbell shape no. 3)

3) Abrasion resistance: Measured by Lambourn tester. Reduction in weightby abrasion indicated by index.

Abrasion resistance (index)=[(reduction in weight in Standard Example10)/(reduction of weight at samples)]×100

Example 1 (Standard Example) and Examples 2 to 3 (Examples of Invention)

These Examples show the results of evaluation of polysiloxanes insystems including silica and carbon black and not including silanecoupling agents. The results are shown in Table II.

TABLE II Ex. 1^(*1) Ex. 2^(*2) Ex. 3^(*2) Formulation (parts by weight)Natural rubber 50.0 50.0 50.0 SBR 50.0 50.0 50.0 Polysiloxane 1 — 2.5 —Polysiloxane 2 — — 2.5 Silica 25.0 25.0 25.0 Carbon black 25.0 25.0 25.0Diethylene glycol 2.5 2.5 2.5 Zinc oxide 3.0 3.0 3.0 Stearic acid 1.01.0 1.0 Antioxidant 6C 1.0 1.0 1.0 Powdered sulfur 2.1 2.1 2.1Vulcanization accelerator CZ 1.0 1.0 1.0 Unvulcanized physicalproperties Kneading performance in mixer X ◯ ⊚ Mooney viscosity 116.890.0 92.8 Vulcanization rate (min.) 14.8 8.5 9.4 Scorching time (min.)16.5 17.0 18.5 Vulcanized physical properties Sheet skin Good Good Good300% modulus (MPa) 9.9 9.9 9.2 Tensile Strength at break 20.6 23.1 19.6(MPa) Elongation at break (%) 497 516 484 ^(*1)standard example^(*2)example of invention.

Example 4 (Standard Example) and Examples 5 to 9 (Examples of Invention)

These Examples show the results of evaluation of polysiloxanes insystems not including carbon black and not including silane couplingagents.

The evaluation was made in the same way as Examples 1 to 3 with theformulations shown in Table III. The results are shown in Table III.

TABLE III Ex. 4^(*1) Ex. 5^(*2) Ex. 6^(*2) Ex. 7^(*2) Ex. 8^(*2) Ex.9^(*2) Formulation (parts by weight) Natural rubber 50 50 50 50 50 50SBR 50 50 50 50 50 50 Silica 50 50 50 50 50 50 Polysiloxane 3 — 5 — — —— Polysiloxane 4 — — 5 — — — Polysiloxane 5 — — — 5 — — Polysiloxane 6 —— — — 5 — Polysiloxane 12 — — — — — 5 Diethylene glycol 2.5 2.5 2.5 2.52.5 2.5 Zinc oxide 3 3 3 3 3 3 Stearic acid 1 1 1 1 1 1 Antioxidant 6C 11 1 1 1 1 Powdered sulfur 1.7 1.7 1.7 1.7 1.7 1.7 Vulcanizationaccelerator DPG 0.5 0.5 0.5 0.5 0.5 0.5 Vulcanization accelerator CZ 1 11 1 1 1 Unvulcanized physical properties Kneading performance in mixer X⊚ ◯ ◯ ⊚ ◯ Mooney viscosity 152.4 81.6 89.2 94 80.4 70.2 Vulcanizationrate (min.) 35.3 12.3 11.4 11.6 10.0 11.1 Scorching time (min.) 11.421.7 25.3 20.9 23.7 30.4 Vulcanized physical properties Sheet skin GoodGood Good Good Good Good 300% modulus (MPa) 3.9 5.8 3.9 3.7 3.7 3.7Tensile Strength at break (MPa) 20.1 22.2 20.2 20.2 20.3 20.4 Elongationat break (%) 723 729 738 745 720 723 ^(*1)standard example ^(*2)exampleof invention.

Example 10 (Standard Example), Examples 11 to 15 (Examples ofInvention), Example 16 (Comparative Examples, and Examples 17 to 21(Examples of Invention)

These Examples show the results of evaluation of polysiloxanes insystems including silica and a silane coupling agent but not includingcarbon black.

The evaluation was made in the same way as Examples 1 to 3 with theformulations shown in Table IV. The results are shown in Table IV.

TABLE IV Ex. Ex. Ex. Ex. Ex. Ex. Ex. 10^(*1) 11^(*2) 12^(*2) 13^(*2)14^(*2) 15^(*2) 16^(*3) Formulation (parts by weight) Natural rubber50.0 50.0 50.0 50.0 50.0 50.0 50.0  SBR 50.0 50.0 50.0 50.0 50.0 50.050.0  Silica 50.0 50.0 50.0 50.0 50.0 50.0 50.0  Silane coupling agent 2.5  2.5  2.5  2.5  2.5  2.5 2.5 Polysiloxane 3 —  2.5 — — — — —Polysiloxane 4 — — 2.5 — — — — Polysiloxane 5 — — —  2.5 — — —Polysiloxane 6 — — — —  2.5 — — Polysiloxane 12 — — — — — 2.5 — Siliconeoil^(*4) — — — — — —  2.5 Zinc oxide  3.0  3.0  3.0  3.0  3.0  3.0 3.0Stearic acid  1.0  1.0  1.0  1.0  1.0  1.0 1.0 Antioxidant 6C  1.0  1.0 1.0  1.0  1.0  1.0 1.0 Powdered sulfur  1.7  1.7  1.7  1.7  1.7  1.71.7 Vulcanization accelerator DPG  0.5  0.5  0.5  0.5  0.5  0.5 0.5Vuicanization accelerator CZ  1.0  1.0  1.0  1.0  1.0  1.0 1.0Unvulcanized physical properties Kneading performance in mixer X ⊚ ◯ ◯ ⊚◯ X Mooney viscosity 101.2  83.6 91.6 86.4 83.2 78.0 86.4  Vuicanizationrate (min.) 21.9 17.7 19.2 21.0 18.3 10.2 12.2  Scorching time (min.)11.8 20.2 12.6 16.4 17.7 11.8 8.9 Vulcanized physical properties Sheetskin Good Good Good Good Good Good Foam 300% modulus (MPa) 10.6 11.110.3 10.7 10.5 10.1 Not Tensile Strength at break 22.3 21.1 21.5 21.422.2 23.1 measurable (MPa) Elongation at break (Z) 476   475   496  491   512   581   Not measurable Abrasion resistance (index) 100   123  104   103   109   101   Not measurable Ex. Ex. Ex. Ex. Ex. 17^(*2)18^(*2) 19^(*2) 20^(*2) 21^(*2) Formulation (parts by weight) Naturalrubber 50   50   50   50   50   SBR 50   50   50   50   50   Silica 50  50   50   50   50   Silane coupling agent  2.5  2.5  2.5  2.5  2.5Polysiloxane 7  2.5 — — — — Polysiloxane 8 —  2.5 — — — Polysiloxane 9 ——  2.5 — — Polysiloxane 10 — — —  2.5 — Polysiloxane 11 — — — —  2.5Zinc oxide  3.0  3.0  3.0  3.0  3.0 Stearic acid  1.0  1.0  1.0  1.0 1.0 Antioxidant 6C  1.0  1.0  1.0  1.0  1.0 Powdered sulfur  1.7  1.7 1.7  1.7  1.7 Vulcanization accelerator DPG  0.5  0.5  0.5  0.5  0.5Vulcanization accelerator CZ  1.0  1.0  1.0  1.0  1.0 Unvulcanizedphysical properties Kneading performance in mixer ⊚ ⊚ ⊚ ⊚ ◯ Mooneyviscosity 83.2 72.3 73.4 80.5 103.3  Vulcanization rate (min.) 15.2 18.518.7 19.8 23.3 Scorching time (min.) 12.8 13.2 13.9 12.7  9.8 Vulcanizedphysical properties Sheet skin Good Good Good Good Good 300% modulus(MPa) 11.0 11.3 10.2 11.1 10.8 Tensile Strength at break 23.6 23.6 22.322.4 21.9 (MPa) Elongation at break (%) 507   507   557   501   523  Abrasion resistance (index) 102   108   120   113   105   ^(*1)standardexample ^(*2)example of invention ^(*3)comparative example ^(*4)siliconeoil (KF99) (made by Shinetsu Chemical Industry)

As explained above, according to the present invention, by mixing intothe rubber composition a polysiloxane containing an alkoxysilyl group(I) or an acyloxysilyl group (II) together with the silica, it ispossible to remarkably improve the processability of the unvulcanizedrubber composition as shown by Examples 2 to 3 and Examples 5 to 9 andby making joint use of a silane coupling agent, the processability ofthe unvulcanized rubber composition is remarkably improved and theabrasion resistance is also improved as shown in Examples 11 to 15 and17 to 21. Note that as shown in Example 16 (Comparative Example), when asilicone oil is mixed in, the rubber sheet foams and cannot be used forpractical applications.

Example II

The other ingredients used in the formulations of the following standardExamples, Examples of the Invention, and Comparative Examples were thefollowing commercially available products:

Natural rubber: RSS#1

SBR: Nipol NS116 (Nihon Zeon)

NP9528 (33.3% oil developed product, made by Nihon Zeon)

NP1730 (33.3% oil developed product, made by Nihon Zeon)

BR: NP1220 (made by Nihon Zeon)

Silica: Nipsil AQ (Nihon Silica)

Silane coupling agent: Si69 (Degussa) (chemical name:bis-[3-(triethoxylsilyl)-propyl]tetrasulfide)

Polysiloxane: Polymethylethoxysiloxane

Carbon black 1: Seast KH (Tokai Carbon)

Carbon black 2: Seast 9M (Tokai Carbon)

Production of Treatment Agent Polymethylethoxysiloxane (i.e.,polysiloxane 13)

100 g of polymethylhydrogensiloxane (KF99 made by Shinetsu ChemicalIndustry) was added dropwise at 70° C. for 1 hour to 75 g of ethanol and100 μl of a 1% isopropyl solution of chloroplatinic acid. After theaddition ended, the solution was made to react for 8 hours to producethe polymethylethoxysiloxane of the following structure formula. Thereactivity was 90%.

Powdered sulfur: 5% oil treated powdered sulfur

Antioxidant 6C: N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine

Vulcanization accelerator CZ: N-cyclohexyl-2-benzothiazylsulfenamide

Vulcanization accelerator DPG: Diphenylguanidine

Zinc oxide: Zinc White no. 3

Stearic acid: Industrial use stearic acid

Preparation of Samples

Of the ingredients shown in Tables V, VI, and VII, first the ingredientsfor mixture in the first step were mixed in a 1.8 liter internal mixerfor 3 to 5 minutes. The ingredients of the second step were mixed intothe master batch discharged when reaching 165±5° C. To this were kneadedthe vulcanization accelerator and sulfur by an 8-inch open roll toobtain the rubber composition. The obtained rubber composition waspressed and vulcanized in a 15×15×0.2 cm mold at 160° C. for 20 minutesto prepare the desired test piece (rubber sheet) and the vulcanizedphysical properties were evaluated.

The test methods for the unvulcanized physical properties and vulcanizedphysical properties of the compositions obtained in the Examples were asfollows:

Vulcanized Physical Properties

1) 300% modulus, tensile strength at break, and elongation at break:Measured in accordance with JIS K 6251 (dumbbell shape no. 3)

2) tanδ: Measured by viscoelasticity apparatus Rheograph Solid made byToyo Seiki Seisakusho at 20 Hz, initial elongation of 10%, and dynamicstrain of 2% (measured at sample width 5 mm and temperatures of 0° C.and 60° C.).

3) Abrasion resistance: Measured by Lambourn tester. Reduction in weightby abrasion indicated by index.

Abrasion resistance (index)=[(reduction in weight in Standard Example30)/(reduction of weight at samples)]×100

Examples 22 to 23 (Standard Example) and Examples 24 and 26 (Examples ofInvention)

These Examples show the results of evaluation of mixtures ofpolysiloxanes and silane coupling agents and mixtures of polysiloxanesand carbon in systems of NR and SBR. The formulations and results of theevaluation are shown in Table V.

TABLE V Ex. Ex. Ex. Ex. Ex. 22^(*1) 23^(*1) 24^(*2) 25^(*2) 26^(*2)First step Natural rubber (RSS#1) 50.0 50.0 50.0 50.0 50.0 SBR (NS116)50.0 50.0 50.0 50.0 50.0 Silica 50.0 50.0 50.0 50.0 50.0 Diethyleneglycol  2.5  2.5  2.5  2.5  2.5 Silane coupling agent —  2.5 —  2.5  2.5Polysiloxane 13  2.5 — —  2.5 — Polysiloxane 13/silane coupling — —  5.0— — agent (1/1) mixture Carbon black 1/polysiloxane (1/1) — — — —  5.0mixture Carbon black 1 — — —  2.5 — Zinc oxide  3.0  3.0  3.0  3.0  3.0Stearic acid  1.0  1.0  1.0  1.0  1.0 Antioxidant 6C  1.0  1.0  1.0  1.0 1.0 Second step Silane coupling agent  2.5 — — — — Polysiloxane 13 — 2.5 — — — Final step Powdered sulfur  1.5  1.5  1.5  1.5  1.5Vulcanization accelerator DPG  1.0  1.0  1.0  1.0  1.0 Vulcanizationaccelerator CZ  0.3  0.3  0.3  0.3  0.3 Vulcanized physical properties300% modulus (MPa)  9.2  9.5  9.7 10.2 10.5 Tensile Strength at break(MPa) 21.6 23.5 24.1 22.8 23.2 Elongation at break (%) 516   560   570  514   537   tanδ (0° C.)  0.54  0.56  0.54  0.55  0.54 tanδ (60° C.) 0.15  0.16  0.14  0.15  0.14 tan δ gradient (0° C./60° C.)  3.60  3.50 3.86  3.67  3.86 Abrasion resistance (index) 100   106   108   100  105   ^(*1)standard example ^(*2)example of invention.

Examples 27 and 28 and 30 (Standard Example) and Examples 29 and 31(Examples of Invention)

These Examples show the results of evaluation of mixtures ofpolysiloxanes and silane coupling agents and mixtures of polysiloxanesand carbon in systems of NR and BR. The formulations and results of theevaluation are shown in Table VI.

TABLE VI Ex. Ex. Ex. Ex. Ex. 27^(*1) 28^(*1) 29^(*2) 30^(*1) 31^(*2)First step Natural rubber (RSS#1) 60.0 60.0 60.0 60.0 60.0 BR (NP1220)40.0 40.0 40.0 40.0 40.0 Silica 20.0 20.0 20.0 20.0 20.0 Diethyleneglycol  1.5  1.5  1.5  1.5  1.5 Silane coupling agent —  1.0 —  1.0  1.0Polysiloxane 13  1.0 — —  1.0 — Polysiloxane 13/silane coupling — —  2.0— — agent (1/1) mixture Carbon black 1/polysiloxane — — — —  2.0 (1/1)mixture Carbon black 1 — — —  1.0 — Carbon black 2 40.0 40.0 40.0 40.040.0 Zinc oxide  5.0  5.0  5.0  5.0  5.0 Stearic acid  1.0  1.0  1.0 1.0  1.0 Antioxidant 6C  5.0  5.0  5.0  5.0  5.0 Aromatic oil 20.0 20.020.0 20.0 20.0 Second step Silane coupling agent  1.0 — — — —Polysiloxane 13 —  1.0 — — — Final step Powdered sulfur  1.0  1.0  1.0 1.0  1.0 Vulcanization accelerator CZ  1.0  1.0  1.0  1.0  1.0Vulcanized physical properties 300% modulus (MPa)  4.3  4.7  4.8  4.5 4.8 Tensile Strength at break (MPa) 16.0 17.8 18.1 17.2 17.9 Elongationat break (%) 758   772   775   761   781   tanδ (0° C.)  0.32  0.33 0.33  0.31  0.33 tanδ (60° C.)  0.26  0.26  0.26  0.26  0.26 tan δgradient (0° C./60° C.)  1.23  1.27  1.27  1.19  1.27 Abrasionresistance (index) 100   103   107   100   106   ^(*1)standard example^(*2)example of invention.

Examples 32, 33, 35 and 37 (Standard Example) and Examples 34, 36, and38 (Examples of Invention)

These Examples show the results of evaluation of mixtures ofpolysiloxanes and silane coupling agents and mixtures of polysiloxanesand carbon in systems of SBR.

TABLE VII Ex. Ex. Ex. Ex. Ex. Ex. Ex. 32^(*1) 33^(*1) 34^(*2) 35^(*1)36^(*2) 37^(*1) 38^(*2) First step SBR (NP9528) 100.0 100.0 100.0 100.0100.0 100.0 100.0 SBR (NP1730) 40.0 40.0 40.0 40.0 40.0 40.0 40.0 Silica20.0 20.0 20.0 20.0 20.0 20.0 20.0 Diethylene glycol 1.5 1.5 1.5 1.5 1.51.5 1.5 Silane coupling agent — 1.0 — 1.0 1.0 1.0 1.0 Polysiloxane 131.0 — — 1.0 — 1.0 — Polysiloxane 13/silane coupling — — 2.0 — — — —agent (1/1) mixture Carbon black 1/polysiloxane — — — — 2.0 — — (1/1)mixture Carbon black 1 — — — 1.0 — — — Carbon black 2 70.0 70.0 70.070.0 70.0 70.0 70.0 Silica^(*3) — — — 1.0 — 1.0 — Zinc oxide 3.0 3.0 3.03.0 3.0 3.0 3.0 Stearic acid 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Antioxidant 6C5.0 5.0 5.0 5.0 5.0 5.0 5.0 Aromatic oil 10.0 10.0 10.0 10.0 10.0 10.010.0 Second step Silane coupling agent 1.0 — — — — — — Polysiloxane 13 —1.0 — — — — — Final step Powdered sulfur 2.0 2.0 2.0 2.0 2.0 2.0 2.0Vulcanization accelerator CZ 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Vulcanizedphysical properties 300% modulus (MPa) 9.8 10.7 10.8 10.5 10.7 10.4 10.6Tensile Strength at break (MPa) 21.9 22.1 22.3 21.9 22.3 21.6 22.3Elongation at break (%) 665 682 682 671 689 680 684 tanδ (0° C.) 0.740.74 0.74 0.73 0.73 0.74 0.73 tanδ (60° C.) 0.37 0.35 0.35 0.36 0.340.35 0.34 tan δ gradient (0° C./60° C.) 2.00 2.11 2.11 2.03 2.15 2.112.15 Abrasion resistance (index) 100 106 107 100 106 100 105 (Notes:^(*1)standard example and ^(*2)example of invention. ^(*3)chargedindependently without being impregnated elsewhere.)

As explained above, according to the present invention, by addingmixtures of a polysiloxane containing an alkoxysilyl group (I) or (II)and a silane coupling agent or inert filler, mixing becomes possiblewithout overreaction with the silanol groups on the surface of thesilica in one-step mixing and the physical properties (tensile strength,abrasion resistance, tanδ) are improved as shown in Examples 24, 26,Examples 29, 30, and Examples 34, 36 compared with Examples 22, 23 and24, Examples 27, 28 and 30, and Examples 22 to 33 and 35. However, thesuperiority of the tanδ balance in the present invention is shown by thesize of the gradient between 0° C. and 60° C.

Example III Example 39 (Reference Example): Preparation ofpolymethylethoxvsiloxane (Surface-treatment agent)

100 g of polymethylhydrogensiloxane (KF99, made by Shinetsu ChemicalIndustry) was dropwise added to 75 g ethanol and 100 μl of 1% isopropylalcohol solution of chloroplatinic acid at 70° C. for one hour and areaction was caused at 80° C. for 8 hours after the dropwise addition toobtain polymethyl ethoxysiloxane having the following structure;

the yield was 90%.

Examples 40-45 (Present Invention) and Example 46 (Comparative)

Polysiloxane surface-treated metal oxide was obtained by bring intocontact the metal oxide shown in Table VIII with 3% acetone solution ofthe polymethylethoxy siloxane obtained above, followed by drying at 80°C. Thus, the polysiloxane surface-treated metal oxide was obtained.

The hydrophobicity of the polysiloxane surface-treated metal oxide wasdetermined as follows.

∘ . . . Substantially all metal oxide floated on the water whenintroduced into water

X . . . Substantially all metal oxide sinked in the water whenintroduced into water.

The results are shown in Table VIII. As is clear from the results shownin Table VIII, sufficient hydropholicity was observed in the case ofExamples 40-45 and the dispersibility thereof in the starting rubber wasgood.

TABLE VIII Ex. 40^(*1) Ex. 41^(*1) Ex. 42^(*1) Ex. 43^(*1) Ex. 44^(*1)Ex. 45^(*1) Ex. 46^(*2) Silica 1) 100 — — — — 100 100 Titanium oxide 2)— 100 — — — — — Clay 3) — — 100 — — — — Kaolin 3) — — — 100 — — —Bentonite 3) — — — — 100 — — Polysiloxane 4)  5  8  5  5  5  3 — KF99 5)— — — — — —  5 ◯ ◯ ◯ ◯ ◯ ◯ X 1) Nipsil AQ (Japan Silica) 2) R820(Ishihara Sougyo) 3) Kanto Kagaku Shiyaku 4) Polysiloxane prepared inExample 39 5) Methylhydrogen polysiloxane ^(*1)Present Invention^(*2)Comparative

Examples 47-51 (Present Invention). Examples 52-53 (Standard) andExamples 54-55 (Comparative)

The components other than the sulfur and the vulcanization acceleratorwere kneaded in a 1.8 later closed type mixer for 3 to 5 minutes andwhen the temperature reached at 165±5° C., the masterbatch wasdischanged. The masterbatch was then kneaded with the valcanizationaccelerator and surfur by an 8-inch open rolls to obtain the rubbercomposition.

The unvulcanized physical properties of the obtained rubber compositionwere measured. Next, the composition was pressed and vulcanized in a15×15×0.2 cm mold at 160° C. for 20 minutes to prepare the desired testpiece and the vulcanized physical properties were evaluated.

The test methods for the unvulcanized physical properties and vulcanizedphysical properties of the compositions obtained in the Examples were asfollows:

Unvulcanized Physical Properties

Scorch time: Time for viscosity to rise 5 points at 125° C. measuredbased on JIS K 6300.

Vulcanized Physical Properties

1) 300% modulus, tensile strength at break, and elongation at break:Measured in accordance with JIS K 6251 (dumbbell shape no. 3)

2) Abrasion resistance: Measured by Lambourn tester. Reduction in weightby abrasion indicated by index.

Abrasion resistance (index)=[(reduction in weight in Standard Example 47or 53)/(reduction of weight at samples)]×100

Example 47 (Standard), Examples 48-51 (Present Invention) and Example 52(Comparative)

These Examples show the results of evaluation of polysiloxanesurface-treated silica and not including carbon black. The results areshown in Table IX.

The surface-treated silica-1, 2, 3 and 4 are those obtained by surfacetreating the surface of silica (Nipsil AQ manufactured by Japan Silica)5, 10, 20 and 30 parts by weight of polymethylethoxy siloxane preparedin Reference Example 39, based upon 100 parts by weight of silica,respectively. The surface treatment was carried out by contacting thesilica with 3% acetane solution of polymethylethoxy siloxane at roomtemperature followed by drying at 120° C.

Example 53 (Standard), Example 54 (Present Invention) and Example 55(Comparative Example)

These Examples show the results of evaluation ofpolymethylethoxysiloxane in the system containing oil extended SBR andcarbon black. The results are shown in Table IX.

TABLE IX Ex. 47^(*1) Ex. 48^(*2) Ex. 49^(*2) Ex. 50^(*2) Ex. 51^(*2) Ex.52^(*3) Ex. 53^(*1) Ex. 54^(*1) Ex. 55^(*3) Formulation (parts byweight) Natural rubber (SMR5L) 50.0 50.0 50.0 50.0 50.0 50.0 — — — SBR(1) 50.0 50.0 50.0 50.0 50.0 50.0 — — — SBR (2) — — — — — — 150.0 150.0150.0 Carbon black (SAF) — — — — — — 70.0 70.0 70.0 Silica (3) 50.0 — —— — 50.0 20.0 — 20.0 Surface treated silica-1 — 52.50 — — — — — 21.0 —Surface treated silica-2 — — 55.00 — — — — — — Surface treated silica-3— — — 60.00 — — — — — Surface treated silica-4 — — — — 65 — — — —Polyrnethylethoxy silane — — — — — 2.50 — — 1.00 Silane coupling agent(4) 2.50 2.50 2.50 2.50 2.50 2.50 1.00 1.00 1.00 Diethylene glycol 2.502.50 2.50 2.50 2.50 2.50 1.00 1.00 1.00 ZnO 3.00 3.00 3.00 3.00 3.003.00 3.00 3.00 3.00 Stearic acid 1.00 1.00 1.00 1.00 1.00 1.00 2.00 2.002.00 Antioxidant (6C) 1.00 1.00 1.00 1.00 1.00 1.00 3.00 3.00 3.00Microcrystalline wax — — — — — — 1.00 1.00 1.00 Powdered sulfur (5% oiltreatment) 1.70 1.70 1.70 1.70 1.70 1.70 2.00 2.00 2.00 Vulcanizationaccelerator (DPG) 1.00 1.00 1.00 1.00 1.00 1.00 — — — Vulcanizationaccelerator (CZ) 0.25 0.25 0.25 0.25 0.25 0.25 2.00 2.00 2.00 Scorchingtime (min.) 7.8 14.4 12.3 12.0 9.9 13.0 24.9 30.3 28.2 300% Modulus 8.910.2 12.9 12.1 9.8 9.9 11.0 11.8 11.5 Tensile Strength at break (MPa)23.4 26.4 22.5 21.3 20.2 24.6 22.2 23.7 22.8 Elongation at break (%) 570580 460 470 540 570 566 575 569 Antiabrasin (index) 100 130 152 122 109126 100 115 112 (1) Nipol NS116 (Nippon Zeon) (2) Nipol 9528 (NipponZeon, 33.33% oil extended) (3) Nipsil AQ (Nippon Silica) (4) Si69(Degussa) ^(*1)Standard ^(*2)Present Invention ^(*3)Comparative

Examples 56-60 (Present Invention) and Example 61 (Standard)

The surface of silica (Nipsil AQ manufactured by Nippon Silica) wasallowed to surface treat with polymethylethyoxy siloxane prepared inReference Example 39 and titanium catalyst (Examples 56-60) in thecompositions shown in Table X at 100° C. for 1 hour. The resultantmixture was extracted with acetone by Soxhlet's extractor and theconversion was determined from the weight thereof the results are shownin Table X.

TABLE X (wt. part) Ex. 56^(*4) Ex. 57^(*4) Ex. 58^(*4) Ex. 59^(*4) Ex.60^(*4) Ex. 61^(*3) Silica 100  100  100  100  100  100  Polysiloxane 1320 20 20 20 20 20 Titanium catalyst 1^(*1)   0.2   0.2  1 — — — Titaniumcatalyst 2^(*2) — — —   0.5  1 — Conversion (%) 91 99 99 99 99 65^(*1)TA-10 (see the structure above) ^(*2)TC-100 (see the structureabove) ^(*3)Standard ^(*4)Present Invention

As is clear from the results shown in Table X, Examples 56-60 using thetitanium catalyst exhibit higher conversions when compared with StandardExample 61.

All the surface-treated silica obtained improved the processability ofthe unvulcanized rubber composition and the tensile stress andantiabrasion of the vulcanized product, when evaluated in the samemanner as in Examples 47-50.

As explained above, according to the present invention, by mixing intothe rubber composition a metal oxide surface-treated with a polysiloxanecontaining an alkoxysilyl group (I) or an acyloxysilyl group (II), it ispossible to remarkably improve the processability (i.e., scorching time)of the unvulcanized rubber composition and 300% modulus and antiabrasionas shown by Examples 48 to 51. Furthermore, as shown in Example 55, whencarbon black and surface-treated silica were formulated, theprocessability (i.e., scorching time) of the unvulcanized rubbercomposition can be improved. As shown in Examples 56-60, the surfacetreatment efficiency can be improved when a titanium catalyst is used.

Example IV

The various polysiloxanes 1 and 2 mentioned above were used the otheringredients used in the formulations of the following standard Examples,Examples of the Invention, and Comparative Examples were the followingcommercially available products:

Natural rubber: RSS#1

SBR (NS116): Nipol NS116 (Nihon Zeon)

SBR (NP9528): Nipol 9528 (Nihon Zeon)

SBR (NP1530): Nipol 1530 (Nihon Zeon)

BR (NP1220): Nipol BR1220L (Nihon Zeon)

Silica: Nipsil AQ (Nihon Silica)

Silane coupling agent: Si69 (Degussa) (chemical name:bis-[3-(triethoxylsilyl)-propyl]tetrasulfide)

Carbon black 1: Seast KH (Tokai Carbon)

Carbon black 2: Seast 9M (Tokai Carbon)

Powdered sulfur: 5% oil treated powdered sulfur

Antioxidant 6C: N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine

Aromatic oil: Aromatic process oil

vulcanization accelerator CZ: N-cyclohexyl-2-benzothiazylsulfenamide

Vulcanization accelerator DPG: Diphenylguanidine

Zinc oxide: Zinc White no. 3

Stearic acid: Industrial use stearic acid

Preparation of Samples

The components other than the vulcanization accelerator and the sulfurwere mixed in a 1.8 liter internal mixer for 3 to 5 minutes. Thevulcanization accelerator and sulfur were kneaded by an 8-inch open rollto the master batch discharged when reaching 165±5° C. to obtain therubber composition. In the case of 2-step mixing, the first stepconsists of mixing in a 1.8 liter internal mixer for 3 to 4 minutes. Themaster batch discharged when reaching 150±5° C. was mixed together withthe remaining components in the second step by a 1.8 liter internalmixer for 3 to 5 minutes. The vulcanization accelerator and sulfur weremixed with the master batch of the second step discharged when reaching165±5° C. by an 8 inch open roll to obtain the rubber composition. Theunvulcanized physical properties of the obtained rubber composition weremeasured.

Next, the composition was pressed and vulcanized in a 15×15×0.2 cm moldat 160° C. for 20 minutes to prepare the desired test piece and thevulcanized physical properties were evaluated.

The test methods for the unvulcanized physical properties and vulcanizedphysical properties of the compositions obtained in the Examples were asfollows:

Unvulcanized Physical Properties

The same as mentioned above.

Vulcanized Physical Properties

1) Carbon/silica dispersion state: Vulcanized rubber was cut by a sharpblade and the surface was observed and evaluated visually and by anoptical microscope (×100, 400).

⊚ . . . Almost no poorly dispersed clumps of carbon and silica (several100 μm diameter) and equal dispersion.

∘ . . . Several poorly dispersed clumps of carbon and silica seenscattered, but otherwise dispersed to certain extent.

Δ. . . Several dozen poorly dispersed clumps of carbon and silica seen,but otherwise dispersed to certain extent.

X . . . Visible powder observable from cut surface. Innumerable poorlydispersed clumps of carbon and silica observed.

2) 300% modulus, tensile strength at break, and elongation at break:Measured in accordance with JIS K 6251 (dumbbell shape no. 3)

3) tanδ: Measured by viscoelasticity apparatus Rheograph Solid made byToyo Seiki Seisakusho at 20 Hz, initial elongation of 10%, and dynamicstrain of 2% (measured at sample width 5 mm and temperatures of 0° C.and 60° C.).

4) Abrasion resistance; Measured by Lambourn tester. Reduction in weightby abrasion indicated by index.

Abrasion resistance (index)=[(reduction in weight at reference testpiece)/(reduction of weight at test pieces)]×100

However, the reference test pieces were calculated as Standard Examples61, 67, and 74 in Tables XI to XIII.

Examples 61 to 62 (Standard Examples), Examples 63 to 64 (Examples ofInvention). and Examples 65 to 66 (Comparative Examples)

These Examples show the results of evaluation of the silane couplingagent, polysiloxane, and single mixture in an NR, SBR system. Theformulations and results are shown in Table XI.

TABLE XI Ex. 61^(*1) Ex. 62^(*1) Ex. 63^(*2) Ex. 64^(*2) Ex. 65^(*3) Ex.66^(*3) (First step) NR (RSS#1) 50.0 50.0 50.0 50.0 50.0 50.0 SBR(NS116) 50.0 50.0 50.0 50.0 50.0 50.0 Silica 25.0 25.0 25.0 25.0 25.025.0 Diethylene glycol 2.5 2.5 2.5 2.5 2.5 2.5 Silane coupling agent 2.52.5 1.2 1.2 1.2 1.2 Polysiloxane 1 — — 1.3 — 1.3 — Polysiioxane 2 — — —1.3 — 1.3 Carbon black 1 25.0 — 25.0 25.0 — — Zinc oxide 3.0 — 3.0 3.0 —— Stearic acid 1.0 — 1.0 1.0 — — Antioxidant 6C 1.0 — 1.0 1.0 — —Powdered sulfur 2.1 — 2.1 2.1 — — Vulcanization accelerator CZ 1.0 — 1.01.0 — — (Second step) Carbon black 1 — 25.0 — — 25.0 25.0 Zinc oxide —3.0 — — 3.0 3.0 Stearic acid — 1.0 — — 1.0 1.0 Antioxidant 6C — 1.0 — —1.0 1.0 Powdered sulfur — 2.1 — — 2.1 2.1 Vulcanization accelerator CZ —1.0 — — 1.0 1.0 Unvulcanized physical properties Kneading performance inmixer X ◯ ⊚ ◯ ⊚ ⊚ Mooney viscosity 91.1 88.2 86.1 87.1 86.3 85.5Vulcanization rate (min.) 16.1 15.6 13.1 13.3 12.9 13.0 Scorching time(min.) 17.7 16.8 18.7 19.1 19.1 19.0 Vulcanized physical propertiesCarbon/silica dispersion state Δ ◯ ⊚ ⊚ ◯ ◯ 300% modulus (MPa) 11.2 13.814.4 13.7 13.6 13.1 Tensile Strength at break (MPa) 22.7 24.3 25.1 24.023.5 24.5 tanδ (0° C.) 0.54 0.55 0.52 0.53 0.53 0.55 tanδ (60° C.) 0.240.20 0.22 0.21 0.22 0.23 Abrasion resistance (index) 100 105 121 117 111109 (Notes: ^(*1)indicates standard example, ^(*2)example of invention,and ^(*3)comparative example.)

Examples 67 to 69 (Standard Examples), Examples 70 to 72 (Examples ofInvention), and Example 73 (Comparative Examples)

These Examples show the results of evaluation of the silane couplingagent, polysiloxane, and simultaneous Mixture in an SBR system. Theformulations and results are shown in Table XII.

TABLE XII Ex. 67^(*1) Ex. 68^(*1) Ex. 69^(*1) Ex. 70^(*2) Ex. 71^(*2)Ex. 72^(*2) Ex. 73^(*3) (First step) NR (RSS#1) 60.0 60.0 60.0 60.0 60.060.0 60.0 BR (NP1220) 40.0 40.0 40.0 40.0 40.0 40.0 40.0 Silica 10.020.0 10.0 10.0 20.0 10.0 10.0 Diethylene glycol 0.5 1.5 0.5 0.5 1.5 0.50.5 Silane coupling agent 1.0 2.0 1.0 0.5 1.0 0.5 0.5 Polysiloxane 1 — —— 0.5 1.0 — 0.5 Polysiloxane 2 — — — — — 0.5 — Carbon black 2 50.0 40.0— 50.0 40.0 50.0 — Zinc oxide 5.0 5.0 — 5.0 5.0 5.0 — Stearic acid 1.01.0 — 1.0 1.0 1.0 — Antioxidant 6C 5.0 5.0 — 5.0 5.0 5.0 — Aromatic oil20.0 20.0 — 20.0 20.0 20.0 — Powdered sulfur 1.0 1.0 — 1.0 1.0 1.0 —Vulcanization accelerator CZ 1.0 1.0 — 1.0 1.0 1.0 — (Second step)Carbon black 2 — — 50.0 — — — 50.0 Zinc oxide — — 5.0 — — — 5.0 Stearicacid — — 1.0 — — — 1.0 Antioxidant 6C — — 5.0 — — — 5.0 Aromatic oil — —20.0 — — — 20.0 Powdered sulfur — — 1.0 — — — 1.0 Vulcanizationaccelerator CZ — — 1.0 — — — 1.0 Unvulcanized physical propertiesKneading performance in mixer X X ◯ ◯ ◯ ◯ ◯ Mooney viscosity 83.2 82.580.1 80.9 78.2 80.5 80.2 Vulcanization rate (min.) 6.9 8.2 6.8 6.1 7.26.4 6.8 Scorching time (min.) 24.7 27.8 25.1 26.7 28.7 26.5 25.8Vulcanized physical properties Carbon/silica dispersion state Δ Δ Δ ◯ ◯Δ Δ 300% modulus (MPa) 4.48 4.29 4.67 4.81 4.62 4.79 4.66 TensileStrength at break (MPa) 17.2 16.0 17.8 18.13 17.2 17.9 17.6 tanδ (0° C.)0.332 0.316 0.334 0.331 0.314 0.328 0.331 tanδ (60° C.) 0.274 0.2630.271 0.274 0.264 0.271 0.273 Abrasion resistance (index) 100 95 103 107106 107 104 (Notes: ^(*1)indicates standard example, ^(*2)example ofinvention, and ^(*3)comparative example.)

Examples 74 to 75 (Standard Examples), Examples 76 to 78 (Examples ofInvention), and Examples 79 to 80 (Comparative Examples)

These Examples show the results of evaluation of the silane couplingagent, polysiloxane, and single mixture in an SBR system. Theformulations and results are shown in Table XIII.

TABLE XIII Ex. 74^(*1) Ex. 75^(*1) Ex. 76^(*1) Ex. 77^(*2) Ex. 78^(*2)Ex. 79^(*2) Ex. 80^(*3) (First step) SBR (NP9528) 100.0 100.0 100.0100.0 100.0 100.0 100.0 SBR (NP1730) 40.0 40.0 40.0 40.0 40.0 40.0 40.0Silica 20.0 20.0 20.0 20.0 20.0 20.0 20.0 Diethylene glycol 1.5 1.5 1.51.5 1.5 1.5 1.5 Silane coupling agent 2.0 2.0 1.0 0.5 1.0 1.0 1.0Polysiloxane 1 — 1.0 1.5 — 1.0 — — Polysiloxane 2 — — — — 1.1 — 1.0Carbon black 2 70.0 — 70.0 70.0 70.0 — — Zinc oxide 3.0 — 3.0 3.0 3.0 —— Stearic acid 2.0 — 2.0 2.0 2.0 — — Antioxidant 6C 5.0 — 5.0 5.0 5.0 —— Aromatic oil 10.0 — 10.0 10.0 10.0 — — Powdered sulfur 2.0 — 2.0 2.02.0 — — Vuicanization accelerator CZ 2.0 — 2.0 2.0 2.0 — — (Second step)Carbon black 2 — 70.0 — — — 70.0 70.0 Zinc oxide — 3.0 — — — 3.0 3.0Stearic acid — 2.0 — — — 2.0 2.0 Antioxidant 5C — 5.0 — — — 5.0 5.0Aromatic oil — 10.0 — — — 10.0 10.0 Powdered sulfur — 2.0 — — — 2.0 2.0Vulcanization accelerator CZ — 2.0 — — — 2.0 2.0 Unvulcanized physicalproperties Kneading performance in mixer X ◯ ◯ ⊚ ◯ ◯ ◯ Mooney viscosity82.5 79.0 76.6 75.6 78.0 76.3 77.1 Vulcanization rate (min.) 16.3 16.514.6 13.3 14.2 14.4 14.9 Scorching time (min.) 24.5 24.9 27.6 27.2 27.627.2 27.5 Vulcanized physical properties Carbon/silica dispersion stateΔ ◯ ⊚ ⊚ ◯ ◯ ◯ 300% modulus (MPa) 9.9 10.8 10.6 10.4 10.7 10.5 10.6Tensile Strength at break (MPa) 21.8 22.0 22.1 22.3 21.9 22.3 22.1 tanδ(0° C.) 0.737 0.731 0.730 0.733 0.729 0.721 0.723 tanδ (60° C.) 0.3660.350   0.356 0.360 0.358 0.365 0.362 Abrasion resistance (index) 100102 11o 115 109 103 104 (Notes: ^(*1)indicates standard example,^(*2)example of invention, and ^(*3)comparative example.)

As explained above, according to the fourth aspect of the presentinvention, by mixing into the rubber composition for a tire tread silicaalong with the silane coupling agent and a polysiloxane of theabove-mentioned formula (III), the processability of the unvulcanizedrubber composition is improved and further the physical properties ofthe vulcanized rubber are equivalent or become better as shown byExamples 63 to 66, Examples 70 to 73, and Examples 76 to 80; when thesilane coupling agent and polysiloxane of formula (III) are added, evenif the silica and carbon are mixed in a simultaneous step, the state ofdispersion of the carbon/silica is improved and equivalent or betterphysical properties are exhibited compared with other mixtures as shownby Examples 63 to 64, Examples 70 to 77, and Examples 76 to 78; and theabrasion resistance is particularly improved, as clear compared withComparative Examples 65 to 66, Comparative Example 73, and ComparativeExamples 79 to 80.

Example V

The following Examples shows the results of evaluation of polysiloxanein systems including various fillers.

The ingredients used in these formulations of the above-mentionedExamples, except for the following, were used, as shown in Table XIV.

Clay 1: Soft clay manufactured by Nihon Talc K.K.

Clay 2: SILKALIGHT manufactured by Takehara Chemical K.K.

Calcium carbonate 1: Light weight calcium carbonate manufactured byMaruo Calcium K.K.

Calcium carbonate 2: Heavy weight calcium carbonate manufactured byMaruo Calcium K.K.

The evaluations were carried out in the same measured as mentionedabove. The results are shown in Table XIV.

TABLE XIV Ex. 81^(*1) 82^(*2) 83^(*1) 84^(*2) 85^(*1) 86^(*2) 87^(*1)88^(*2) 89^(*1) 90^(*2) 91^(*1) 92^(*2) 93^(*3) Formulation (Part byweight) NR — — — — — — — — 100 100 100 100 100 SBR 100 100 100 100 100100 100 100 100 100 — — — Polysiloxane 3 — 10 — 10 — 10 — 10 — 10 — 3.57.1 Carbon black — — — — — — — — — — 60 60 60 Clay 1 100 100 — — — — — —— — — — — Clay 2 — — 100 100 — — — — — — — — — Calcium — — — — 100 100 —— 100 100 — — — carbonate 1 Calcium — — — — — — 100 100 — — — — —carbonate 2 Zinc oxide 3 3 3 3 3 3 3 3 3 Antioxidant 1 1 1 1 1 1 1 1 1 11 1 10 Stearic acid 1 1 1 1 1 1 1 1 1 1 — — — Powdered sulfur 1.5 1.51.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 6 6 6 Valcanization 1.7 1.7 1.7 1.7 1.71.7 1.7 1.7 1.7 1.7 0.7 0.7 0.7 accelerator Unvalcanized physicalproperty Kneading Δ ◯ Δ ◯ ◯ ◯ ◯ ◯ Δ ◯ ⊚ ⊚ ⊚ performance in mixer Mooneyviscosity 62.4 51.2 55.8 44.2 63 55.8 56.2 49.6 72.8 62 56.4 47.2 39.4Vulcanization 12.4 12.32 14.93 14.53 11.46 11.41 9.79 9.63 3.25 3.215.29 15.37 15.24 rate (min.) Scorching time more more more more moremore more more 16.4 17.8 30.2 31.9 33.2 (min.) than 50 than 50 than 50than 50 than 50 than 50 than 50 than 50 Vulcanized physical property300% modulus 2.26 2.11 3.26 3.3 1.91 1.5 1.39 1.31 3.46 3.66 20.76 19.2618.01 (MPa) Tensile Strength 4.1 4 11 11.2 5.9 5.8 2.8 2.9 15 16.2 21.720.9 at break (MPa) Elongation at 533 538 687 684 627 573 523 523 581660 317 330 302 break (%) ^(*1)Standard Example *2Present Invention

What is claimed is:
 1. A rubber composition for a pneumatic tire treadcomprising (i) 100 parts by weight of at least one rubber selected fromthe group consisting of natural rubber, polyisoprene rubber,styrene-butadiene copolymer rubber, polybutadiene rubber,acrylonitrile-butadiene copolymer rubber, butyl rubber, a diene rubberand ethylene-propylene copolymer rubber, (ii) from 2 to 80 parts byweight of carbon black, (iii) from 5 to 80 parts by weight of silica,(iv) a sulfur-containing silane coupling agent, and (v) a polysiloxanehaving a number average molecular weight of 200 to 100,000 and having arepeating unit of the formula (III): wherein R³ represents independentlya methyl group, an ethyl group, or a phenyl group, R⁴ representsindependently hydrogen or a substituted or unsubstituted alkyl group, R⁵represents an alkyl group, m is 0 or an integer of 1 or more, and n isan

integer of 6 or more.
 2. The rubber composition of claim 1, wherein theamounts of the polysiloxane and silane coupling agent are defined by:(i) 0.5≦(W_(PS)/W_(SC))≦7; and (ii) amount of silica×1 wt%≦W_(PS)+W_(SC)≦amount of silica×40 wt % wherein, W_(PS) is the amountof the polysiloxane in parts by weight, and W_(SC) is the amount of thesilane coupling agent in parts by weight.
 3. The rubber composition ofclaim 1, wherein the components (i)-(v) are simultaneously mixedtogether at a temperature of at least 120° C. to obtain the composition.4. The rubber composition of claim 1, wherein the polysiloxane has thefollowing formula (IV):

wherein R³ represents independently a methyl group, an ethyl group, or aphenyl group, R⁴ represents independently hydrogen or a substituted orunsubstituted alkyl group, R⁵ represents an alkyl group, m is 0 or aninteger of 1 or more, and n is an integer of 6 or more and (iv) asulfur-containing silane coupling agent.
 5. The rubber composition ofclaim 1, wherein said sulfur-containing silane coupling agent isselected from the group consisting of: (a)bis-[3-(triethoxysilyl)-propyl]tetrasulfide, (b)3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, (c)trimethoxysilylpropyl-mercaptobenzthiazoletetrasulfide, (d)thiethoxysilylpropyl-methacrylate monosulfide, and (e)dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide.
 6. Therubber composition of claim 1, further comprising (vi) a vulcanizationsystem composed of sulfur and a vulcanization accelerator.
 7. A rubbercomposition comprising (i) at least one rubber selected from the groupconsisting of natural rubber, polyisoprene rubber, styrene-butadienecopolymer rubber, polybutadiene rubber, acrylonitrile-butadienecopolymer rubber, butyl rubber, a diene rubber and ethylene-propylenecopolymer rubber, (ii) a filler, (iii) a polysiloxane (A) having one ofthe following structures and an average degree of polymerization of 3 to10,000:

wherein, R³ independently represents a methyl, ethyl or phenyl group, R⁵represents an alkyl, R⁶ represents an alkylene group, k is at least 6and p is at least 2 and (iv) a sulfur-containing silane coupling agent(B).
 8. The rubber composition of claim 7 comprising (i) 100 parts byweight of said at least one rubber, (ii) from 5 to 100 parts by weightof silica, and (iii) an amount of a rubber compounding agent comprisingthe polysiloxane (A) and the sulfur-containing silane coupling agent (B)in a ratio of (A)/(B)=95/5 to 5/95 to give a content of the polysiloxanecontained therein of 0.2 to 30% by weight based on the totalcomposition.
 9. The rubber composition of claim 7, wherein said filleris a silicon-containing filler.
 10. The rubber composition of claim 7,wherein the polysiloxane is contained in an amount of 100% by weight orless based on the total amount of the filler.
 11. The rubber compositionof claim 7, wherein the sulfur-containing silane coupling agent ispresent in an amount of 40% by weight or less based on the total amountof the filler.
 12. The rubber composition of claim 7, wherein saidsulfur-containing silane coupling agent is selected from the groupconsisting of: (a) bis-[3-(triethoxysilyl)-propyl]tetrasulfide, (b)3-trimethoxysillpropyl-N,N-dimethylthiocarbamoyltetrasulfide, (c)trimethoxysilylpropyl-mercaptobenzthiazoletetrasulfide, (d)thiethoxysilylpropyl-methacrylate monosulfide, and (e)dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide.
 13. Arubber composition comprising (i) at least one rubber selected from thegroup consisting of a natural rubber, polyisoprene rubber,styrene-butadiene copolymer rubber, polybutadiene rubber,acrylonitrile-butadiene copolymer rubber, butyl rubber, a diene rubberand ethylene-propylene copolymer rubber, (ii) a filler, and (iii) apolysiloxane having the following formula (IV):

wherein R³ represents independently a methyl group, an ethyl group, or aphenyl group, R⁴ represents independently hydrogen or a substituted orunsubstituted alkyl group, R⁵ represents an alkyl group, m is 0 or aninteger of 1 or more, and n is an integer of 6 or more.
 14. The rubbercomposition of claim 13, wherein said filler is a silicon-containingfiller.
 15. The rubber composition of claim 14, wherein the polysiloxaneis contained in an amount of 100% by weight or less based on the totalamount of the filler.
 16. The rubber composition of claim 13, whereinthe sulfur-containing silane coupling agent is contained in an amount of40% by weight or less based on the total amount of the filler.
 17. Therubber composition of claim 13, further comprising (v) a vulcanizationsystem composed of sulfur and a vulcanization accelerator.